The present invention relates to an endoscope system, an imaging apparatus, a control method, and the like.
An imaging apparatus such as an endoscope may be required to generate a deep-focus image inside a body cavity in order to facilitate a doctor's diagnosis. This has been achieved by increasing the depth of field of an endoscope by utilizing an optical system having a relatively large diaphragm value (hereinafter may be referred to as “F-number”).
In recent years, an imaging element having about several hundred thousand pixels has been used for endoscope systems. The depth of field of an optical system is determined by the size of the permissible circle of confusion. Since an imaging element having a large number of pixels has a small pixel pitch and a small permissible circle of confusion, the depth of field of the imaging apparatus decreases. In this case, the depth of field may be maintained by increasing the diaphragm value of the optical system. According to this method, however, the optical system darkens, and noise increases. Therefore, the image quality deteriorates. Moreover, the effects of diffraction increase as the diaphragm value increases, so that the imaging performance deteriorates. Accordingly, a high-resolution image cannot be obtained even if the number of pixels of the imaging element is increased.
JP-A-10-225427 aims at obtaining a practical depth of field by increasing the size of the permissible circle of confusion along with a change in diaphragm value, and changing the reading pixel size of the imaging element to be almost equal to the size of the permissible circle of confusion. A sufficient depth of field is thus obtained while ensuring a sufficient quantity of light when imaging a dark object.
JP-A-8-181909 discloses suppressing a change in resolution based on the diaphragm value. In JP-A-8-181909, a constant resolution is obtained independently of the diaphragm value by decreasing the degree of contour enhancement when decreasing the diaphragm value of the optical system, and increasing the degree of contour enhancement when increasing the diaphragm value of the optical system.